Anyway: it’s still moot. What she did, even based on your account, is not illegal.
It’s not illegal to apply for TN, period. If the application is rejected, that doesn’t make the application retroactively illegal.
It’s not even illegal for a Canadian to apply for a TN at the border crossing, have their application rejected, and keep driving right into the US. I know this because it happened to me. As Canadians don’t need work permits to enter the US, entering the country wasn’t the question - only working in it.
Unless she’d previously been given paperwork that had banned her from entry to the US - and she hadn’t been - there was nothing illegal with reapplying. She was told to reapply.
Whether she did anything “wrong” is debatable, but whether she did anything illegal isn’t.
Guards/cops/whatever maybe be dumb sometime but they don't say this when everything is done correctly. If she had just made an honest mistake, she would have been told so and corrected. But clearly, she tried to do something that wasn't allowed or played with the lines on how things have to be done. Then she complains that she got detained for it. If you don't respect the rules, there are consequences, women tend to forget it because they get away with all kind of shit in today's society.
Also, The Guardian has a habit of obfuscating the truth (by omitting facts or orienting the narrative) to create outrage, so it doesn't surprise me at all.